Glasses with good infrared absorption are usually produced by reducing iron present in the glass to the ferrous state or by adding copper. Such materials give glasses a blue color. The materials added to achieve good ultraviolet radiation absorption are Fe.sup.3+, Ce, Ti or V. The quantities added to cause the desired level of ultraviolet absorption are such as to tend to color the glass yellow. The combination in the same glass of both good UV and good IR absorption gives glasses whose color is either green or blue. Proposals have been made to produce vehicle glazings with good protection against IR and UV radiation in gray or bronze, but the proposed glasses tend to have a greenish yellow tinge.
Prior art heat absorbing glasses which are neutral and of a blue, green, gray or bronze tint tend to have considerably higher solar light transmittances than would be desirable in privacy glazings. For example, U.S. Reissue Pat. No. 25,312 is directed to a gray glass composition containing 0.2 to 1 percent Fe.sub.2 O.sub.3, 0.003 to 0.05 percent NiO, 0.003 to 0.02 percent CoO and 0.003 to 0.02 percent Se and having a visible transmittance of between 35 and 45 percent at 0.25 inch thickness.
A typical dark gray prior art glass has the following composition: 72.9% SiO.sub.2, 13.7% Na.sub.2 O, 0.03% K.sub.2 O, 8.95% CaO, 3.9% MgO, 0.10% Al.sub.2 O.sub.3, 0.27% SO.sub.3, 0.06% Fe.sub.2 O.sub.3, 0.015% CoO and 0.095% NiO. Solar energy absorption of this type of glass is not as low as would be desired for the purposes of the present invention.
More recently nickel-free heat absorbing gray glasses have been proposed for use in low transmittance glazings. Examples of these glasses may be found in U.S. Pat. Nos. 4,104,076 and 5,023,210. However, both of these patents include chromic oxide as a coloring agent, may require the use of melting operations/apparatus other than conventional overhead fired tank-type melting furnaces to provide the reducing conditions during melting necessary to produce the desired glasses, and have colorant concentrations of iron oxide, cobalt oxide and selenium that would not produce the particular combination of properties desired here.
The most promising glazings found to date to be suitable for use in privacy applications require glass substrates having films or coatings thereon to achieve the desired properties. An example of one such particularly effective glazing is described in U.S. Pat. No. 5,087,525 to R. D. Goodman and P. J. Tausch. While these filmed glazings are indeed beneficial and enable "fine tuning" of spectral properties, it would be advantageous, particularly from a cost standpoint, to produce a glass composition which by itself would provide a desired mix of properties for privacy glazings.